Various types of power converters can be designed to convert a source of direct current from one voltage level to another voltage level. As an example, a buck converter is a class of switched-mode power supply that typically includes transistors configured to step down an input voltage to provide a corresponding output voltage to one or more storage elements, such as including a capacitor and/or an inductor. A common application for a buck converter is battery charger. For example, the battery charger is configured to put energy into a battery by forcing an electric current through the battery. When in normal operation, a synchronous buck converter draws current from the input and pushes current out of the output. Forced continuous conduction mode (CCM) operation is desired in some applications for its frequency response and design simplicity. However, in this mode, a controller may request current in the reverse (negative) direction. Current in the negative direction is called boost-back and is generally undesired in a buck regulator.
By way of example, boost-back may be categorized into two general types: regulated boost-back and unregulated boost-back. A regulated boost-back condition occurs when the converter is able to request a negative current and find a stable regulation point. Unregulated boost-back occurs when the converter requests negative current but is unable to reach a stable operating point. This condition can cause uncontrolled voltage and/or current run-away on the input of the converter and may damage the device or other components in the system. The regulation loops in the converter most often responsible for unregulated boost-back are output voltage regulation and temperature regulation. For temperature regulation, if the ambient temperature exceeds the target junction temperature regulation point, then this regulation loop will drive the output current below zero and continue to drive the current lower (more negative). This condition is a positive feedback condition, which is undesirable, since the more negative current the converter drives out, the more heat the device dissipates.